Boundary-based passive component inspection approach using eigenvalues of covariance matrices

A boundary-based scheme to inspect basic dimensions and surface defects on solder plates (terminations) of passive components by using the eigenvalues of covariance matrices was developed. The image of the passive component was initially processed to show only two terminations. The eigenvalues of covariance matrices for boundary points, which are equivalent to curvature measurements, then generate a one-dimensional representation describing the angle variations on termination boundaries. Since a single corner (intersection of two boundary edges) and jagged corners (a surface defect) are local deviations on termination boundaries, their locations will be represented as highly fluctuating eigenvalue waveforms. By setting an appropriate threshold on the eigenvalues, the surface defects and single corners on the termination boundaries can be identified. The basic dimensions of a passive component are determined simply by the distances between the detected single corners. Real passive components (0805 MLCCs) are testing samples to evaluate the performance of the proposed approach. Experimental results show that the proposed approach achieves precise identification for surface defects and measurement for the basic dimensions. The proposed approach is precise, rotation invariant and template free. Therefore, it is especially suitable for small batch production of various types of passive components.